Image modifier



Aug. 19, 1930. A. AMES, JR., Er AL 1,173,335

IMAGE MODIFIER Filed June L21. 1922 z2 9 Z za lzenons: deZ bari mes J'r'. Charles' /Cl P ocor K.

y 'o m Patented Aug. 19, 1939 wan-s Apinicatimi' ifiid ,frane fai,

f This invention relatesto an-image inediiier adapted to change the vcharacter-oi'the image formedbyan obj ectivelensyand usefful 'for ,the purpos'eof altering thev characterk5 ilstics of such anV i`1na'ge,-1and*to the art of making'such imager'modi'eris. 'y

In photographyit may be desiredfto :alter the character of the image gin a1 primary sense,`-Wlien the images are of the naturalob- 1g jectsfand' the altered image fis-to vbe impressed upon -a plate to fform photographicpi'cture orf inV photography.' it fmay ldesired `to alter the-charactcristics' of theprevious nega- 't'iv'e or fpositive `photograph "by lmaking` a i5 copy, and in that casetheimageimodiied is a vsecondary'imagegf'or-it may be desired to project'apositive-picture upon a screen for visual purposes, and in that casethemodiflication of the image would b'e-1tertiary,ffand 20 iii-respect to the ultimate thing,` tofb'eviewed ybyy the observer ofthe picture, i. e., thescreen image.' Y l rThe Acharacter of change ormodili'cation inf the 'image Whether primary, secondary, l`or ayt-ertiary, andor-ivhich-the device of this yinvention isipar'ti'cularly adapted, is Vto spro- -duce an l:a'ppronimationottf the image characteristic of the normal ocular retinal impression. While We have describedindetail sathe"characteristics of these visual Aimpressionselsewhere, it Will suffice forl the prcsent purposes to mention that the rvisual acuity of the peripheral. parts 4of. the ret-ina lis not yas good as it is at the fovea centrali's or clearseeing ar'ea upon Which theobjects 1t-Which kWe are looking directly, vand which =have our Vmentalattention, are imaged. Atan angle yof 20 away from this center ofattention Vvisual acuity is much reduced; it approximates ythe v'average to say that atfthe iiovea centralis the 'deiinitionis about'iortytimes betterthanfit is 200 away rom=tlieaxis`. lThe blurring andlack of vacuity.-o'iif'vision awayffrom'theaxis maybe' assigned to two causes ;lir'st tothe oblique aberrationsfofthe "lens-system' 'of the eye'; and second, to 'the lac'lcof sen'sitiveness or physio'lo,f:,rical` resolvingipoiver-fof the retinal surfacezits'elfin'its 'outlying portions. Anatomicall-y, `vthe cones -of -the lro'd-a'nd-cone lnervous 'system ofr'the departure romtlie axis.

i522. serial No. 569,992. i y retina are spaced much further apart inthe outlying parts of the retinathan they are at the clear-seeing part. Y

l/le have by research determ`ned.theoptical losses of theflens system` of the eye with respect to sharpness andthe vphysiological losses-in respectfto lack of retinal sensitiveness atthe outlyingrportions of theretina, andzconclude that at :200' from Vthe axisthe lack of .-deinition, asmeasuredbythe error oi' sharpness of thel test object, should be about Jfortyy times that at.l and` near-the axis.-

For' practical. approximative purposesthe clear-seeingfarea of vision maybe considered to be about-Go avide horizontally and about 4 lhigh vertically at. the. maximum, and 1be.- yond, this area the deiinition los/ses :gradually fincreaseabout ini proportion to the angle of For the various purposes-above mentioned,

i.-e.,,forphotography or the `display ofphotographs,the existing practices are `not'fortunate in several respects. Untill recently, the.`attempt of photographers was to pro- -duce,fwith''tlie aid of elaborately corrected lenses, Yivorked under small aperture, rand iwithplates capable fofcdiscrimination of fine detailfapictureof which every part was defined'to thelimitof accuracy (of the optical,

cently abetterlconsideration of the aesthetics y ofportraitandxlandscape photography, es-

pecially asl induced by the great increase in the luse `of photography for imotion picture purposes, has led even the average' photographer .tosee thatA what may be `referred to asthe broad and Whole visualcontent ofany picture is not to be' reache'd by a photolgraph'in detail of every part of the field of view'. The remedies-heretofore offered have comprised numerous schemes `for blurring /tlresimage' of .the lphotographic lens, for eX- ampl'eby lthe. so-called ysoaitiocus lenses such as Dallmeyers classic contribution along this line, and a number of secondary devices such as printing the images with the negative and the printout of contact, not to mention the familiar expedients for vignetting either the primary image, or the print, or the positive, for the purpose of Vobtaining a certain approximate concentration upon the interesting part of the picture to which attention was to be directed. Motion picture photographers, for instance, have in common practice used dark colored screens of chiffon, with a hole in the center` in front of the taking lens, and there have been other c expedients of this nature, without wholly satisfactory results. This is because in pictures made by any of these expedients, the picture is defective either in that the loss of detail does not gradually fall off from the center outward, or that the loss of detail does not fall off to the same extent and in the same way that it does in the eye; or that the diffusing means obstructs the light or breaks it up to such an extent that a large part of it does not reach `the plate, with the result that there is under-exposure at the outer parts of the plate or over-exposure at the center of attention. It will be obvious that, although the definition should decrease away from the center of attention, the monochromatic values (and the color in the case of the color photographs) should be correctly pictured if the photograph is to be satisfactory.

Objects of the present invention are to provide a way of producing approximately the effect of the normal visual impression by simple means adap-ted to be used with the ordinary camera, enlarger, printer, copying camera, or projection apparatus, for the purpose of either primarily, secondarily, or finally producing from animageotherwise too exact in its outlying parts an image exact at the center of attention, and diffused quantitatively to the correct'extent to correspond to visual impression at outlying parts of the picture.

We shall now describe with the aid of the accompanying drawings one example only of an image modifier corresponding to the invention, by way of illustration of the genus which it exemplifies, and the best mode known to us of preparing this instrument. In the drawings, Fig. 1 is a face View indicating the principal features of an image modifying screen corresponding to the invention:

Fig. 2 is a typical section on an exaggerated vertical scale through the center of the screen shown in Fig. 1;

Fig. 3 is a very much enlarged elevation of a detail of the surface toward the margins of the screen, showing the appearance of the screen againsta bright background;

Fig. 4 is an enlarged section corresponding to the part of Fig. 3 showing the nature of the surface irregularities;

Fig. 5 is a diagram illustrating a preferred relation of the image forming lens, the screen, and the photograph;

Fig. 6 is a diagram which will serve to indicate, but not to show, the qualities of the modified image, and

Fig. 7 is a side elevation, the screen being shown in vertical section, illustrating steps in the preferred mode of making the same.

Referring now to Figs. 1, 2, 3, and 4;, the screen 1 comprises a vrelatively thin piece of. clear glass as nearly plane on its surfaces and having its surfaces as nearly parallel as may beprocured, for instance, by selection from such glass as is in common use for lantern slides and small photographic plates. The thickness of the screen 1 may be selected roughly in accordance with the focal length of the camera or projector with which it is to be used; for a small camera such as a motion picture camera, for instance, having focal distances of about fifty millimeters, the screen should be in the neighborhood of about a millimeter or less in thickness, but a thicker screen can he used for hand cameras, and a still thicker screen used for the larger cameras employed for landscape and portrait photography, if desired.

In the center of the screen a plane parallel spot 2, which may be longer laterally thanit is vertically, is arranged to occupy about 4 in the height and 6 in the width of the cone of image bearing rays from the lens L with which the screen is to be used. It will be understood that these proportions are-not exact, and that they can be modified within limitations by moving the screen, see Fig. 5, nearer to or farther away from the lens, but the preferred' general position of the screen is nearer the plate P on which the image is formed (or the positive to be projected) than it is to the lens L by which the image is formed, and the separation between the plate P and the screen 1 is that sufiicient for purposes presently explained. As indicated in Fig. 5 the screen 1 may be Vmounted rigidly vertically and laterally with the lens L in order to be adjustable, for instance, by the telescoping slide 3, 4, toward and away from the lens, and thus be adapted to be moved with the lens in respect to the plate or film P, in order to shift the position of the plane parallel portion 2 of the screen in respect to the plate, without shifting portion 2 away from the optical axis of the lens.

Proceeding in any radial direction from the center 2, the screen 1 is provided with a polished, irregularly undulating surface 12, deviating, as the center is proceeded away from, more and more from the plane 10 of that surface of the screen 1, so that the individual slopes of the undulations of the surface are at greater and greater angles with leraars-e5 respect to the unaltered plane 11 of the lower side of the screen 1. Considering this formation as a system of waves rendered xed, the effect desired may comprise a gradual lessening of the wave lengths, the amplitude remaining the same; or a gradual increase in amplitude, the Wave length remaining the same, or both, the-assumed propagative direction of the waved surface. being radial from the center. In fact, the virtual waves are not simple, but comprise complex undulative surfaces, of Which'the average angular deviation increases proportionally to the radial distance from the center.

The undulations or irregularities of the surface are indicated at 12 in Figs. l, 2 and 4, but it will be understood that the draw'- ings are greatly exaggerated in their vertical dimension.

, The purpose and effect of the undulations 12 is best indicated in Figs. 4 and 5.V They serve to cause refractive deviations, and are in the nature of minute prisms or lenses, having an exceedingly small refractive effeet, but nevertheless serving to bend the rays converging from the margins of the aperture of the lens L to a focus at the plate P differently in respect to each intercept of thescreen with anyv such cone of rays, so that light otherwise proceedingy to a focus on the plate P will not be focused, but will be variously refracted, to an extent depending uponl the magnitude of theldeparture from plane parallel surfaces of the portion of the screen intercepted by the particular cone in question. As mentioned, the effective angle and therefore deviatio-n of the prismatic for lenticular surface of the screen 11, if we consider any integral unit of this screen, will vary inproportion to its distance from the plane parallel center 2. VThe optics of the screen 2 will be understood from Figs. 4 and 5, and from Fig. 3, which illustrates, greatly magnified, an area near one of the margins when viewed against an evenly ilhuninated background. The darker spots in y Fig. 3 represent li ht distributed away from the line of view o the screen and the lighter spots represent light gathered into the line 'of view.

In order to be eective, the angular deviation away from focusing'position of the rays of light coming from the lens L must have a maximum corresponding to the intended diusion of the image and no more. Otherwise light at the margins of the plate P would be lost by being distributed out of the image; otherwise, no matter how small the recurring dimensions of the prisms and lenses of the screen surface 12, there will be insuficient regularity in the blurring of the images to provide an even illumination roughly corresponding to the values of the surface of the picture, and the picture will be mottled, which is not-desired. What is desired is to H LReferring now to F,

'diffuse'ithe images, especially images ff enges between flight and -,dark fpoaiens ref tfhe'fpicture, 'so as to i make such :ledges iahoi'it .twenty to @fortytimes wider thanfthey'fwill 'be in i the center `-of *the-picture ifoppositeithe l y7e make. screens having these effectsfby-the lfllowing preferred method p g. -7iarpiecefof1 selected near-ly planeand'f nearly paralleli Iglass k' (co'rrect plane andiparallel-)glassbeingof lcourse more desirable but unnecessaril'yiexpensive) isf'protected on the'back surface'll, andat the v 'margins-at 1'6 and the center at17',by cov-k ering -vvithl a tliinfc'oat f'fbituminous-varnish, such-as any'l etchers-fground, and placed ina.

lbath 15. The -surfaces ofithe glass l-platel should-be chemically clean. The' bath is now filled with 1an aqueous solution of 'hydro- -fluoric acid, preferably comprising-about equal .portionsv yof lcommercial hydroiuo'ric 'acid lof normal lstrength yand distilled water. lhe operator j-after about five minutes,'1-m'oreor i' less, 4flays 11 in l contact'with 'the vspot `j1'7 an-air-inflated yrubber -ball 18 `which vdle or arm19 to enable it to be manipulated more-easily, andfthen presses vdownward in 'the `v`direction of lthe Sla'rrow -A slowly fand `Stea`dily,-"at such fa rate that "-at 5the lend i of on? the fplate 1J is reduced yto. an exceedingly *thin iiilm, 1 and in i the *described way this:` expulsion ofi yt-hea'cidfromtheisurface 12 profceeds radi-ally outward from the fcenteriof the screen. VVhentheball has-rached'fthe marg'insi'o'ftheiplate (it-is not'A necessary that itf shouldreachfthe corners) fthe 'ball'iis :sud- Ldenly'fz-em'oved and -the plate 71 `is quiclrly --dro-pped'iinto La ylarge quantity of water, -washed viin #clean Jwater, rkand the etchers ground #at 16 @and 17 l and 'on thehack of: the

plate removed.

The-1 result is nowf'n'ot, asi might he expected, a plate having a frosted'surface. :We'n'd that asiso treated, 4Vthe-upper surface of the f plate-has'- the 1 desired -undulations 12 which remain polished. We attribute this to the r about ten to twenty-minutes l{(more 1f or less, .depending uponi the strengthofithe-facid, the

TOC

describedl way of stopping the action of the i acid, b v reducing it to a thin film, which is soon exhausted by chemical combination vvith'` the glass and leaves the etched surface in the irregular but-smooth state characteristic of the wet, surfaces of glass While under solution in the acid. Whatever, the cause, the

effect is the desired effect. The parts of the 'screen adj acent to the center 2 are barelyafected by the acid; the outlying pai-ts are considerably aifected. The longer `the acid is :allowed to act (i. Ae. the slower the forcing downward of the compressed ball 18) the Vmore refractive Will be the outer surfaces of lthe glass.. y

The screen isA now completed y by local grinding and polishing of the spot 2 to re'- inove the linear margin always found around `the etchers ground resist at 17. .l

We claim; 1. An image modiiier.

trai clear spot not adapted to irregularly retract incident light, andl 'a surrounding region containing refractive surfaces irregularly oriented in all directions, the Said screen having an increasing refractive effect toward the margin ofthe screen.

A glass image modifier screen having a central clear spot not adapted to` irregularly retract incident light, and having on one surface a surrounding regio-n containing etched refractive surfaces oriented in all directions, the said screen having an increasing reiiiactive effect toward the margin of the screen.k j v.

3. A transparent sheetliaving a polished surface substantially parallel with the other surface in one spot, and repeatedly, progressively and irregularly deviating from paral lel in every direction as said spot is departed 4. A inodiierfforuse Wit-li image oriners f' .i'or the purpose of diffusing the image in varying degrees in accordance with angular departure from the axial region of the image consisting of a substantially plane parallel glass screen having unchanged surfaces at and neara portion through which the axial region of the ,image is to .be formed, and having an etched surface increasingly ,at iected by the etching in concentric regions, in accordance With the several diameters of said regions. 1

5. The combination With an image-forming lens and an image'receiving screen of a trans- A parent refractive image modifier having an ineffective axial region and outlying regions of irregular undulation placed in the imagebearing light nearer to the r ceivingfscreen than to the image-forming lens.

Signed by us' at Hanover, N. H., this sii:- teenth day of June, 1922. v

ADELBERT AMES. JR.

V(punis. A. Piiooro'ii.

screen having a cen- 

